Historic lead levels from the era of leaded gasoline may be contributing to cognitive issues 50 years later, suggests research reported for the first time at the Alzheimer’s Association International Conference, which took place in Toronto and online.

Americans are about 20% more likely to experience memory problems if they lived in areas with high levels of atmospheric lead between 1960 and 1974, according to the analysis of more than 600,000 adults 65 and older.

“Research suggests half the U.S. population — more than 170 million people — were exposed to high lead levels in early childhood. This research sheds more light on the toxicity of lead related to brain health in older adults today,” said Maria C. Carrillo, Ph.D., Alzheimer’s Association chief science officer and medical affairs lead.

“Other studies suggest that lead exposure at any point in life may cause cognitive problems; it may be more likely to affect certain populations and reflect disparities; and there is a biological connection between lead exposure and Alzheimer’s.”

LEAD AIR POLLUTION ASSOCIATED WITH MEMORY PROBLEMS 50 YEARS LATER

In a first-of-its-kind study, researchers examined how exposure to airborne lead from 1960 to 1974 — when leaded gasoline use was at its highest — may affect brain health later in life. They determined that older adults who grew up in areas with moderate to extremely high historical atmospheric lead levels were about 20% more likely to report memory problems as adults 50 years later.

The researchers calculated the average historical atmospheric lead levels by area and linked it to self-reported memory problems from the American Community Survey from 2012-2017 (368,208 people) and 2018-2021 (276,476 people).

They didn’t analyze the source of the lead, but believe that the higher the density of automobile traffic, such as in urban areas, the higher the atmospheric lead. Factoring in both time periods, the researchers determined that 17% to 22% of people living in areas with moderate, high or extremely high atmospheric lead reported memory issues.

“Our study may help us understand the pathways that contribute to some people developing dementia and Alzheimer’s disease,” said Eric Brown, M.D., MSc, FRCPC, lead author of the study, associate scientist and associate chief of geriatric psychiatry at the Centre for Addiction and Mental Health, Toronto.

Lead was originally added to gasoline to increase performance until researchers determined it posed serious risks to health and the environment. The phase-out of leaded gas began in 1975 when all new cars sold in the U.S. were required to have catalytic converters.

While the risk of atmospheric lead has decreased, other sources of exposure remain, such as old lead paint and pipes. Those who have been exposed to atmospheric lead should focus on reducing other risk factors for dementia, including high blood pressure, smoking and social isolation, said Brown.

STUDY REVEALS HOW LEAD EXPOSURE MAY SET THE STAGE FOR ALZHEIMER’S

Even low levels of lead exposure can create permanent changes in brain cells, including increased buildup of abnormal tau and amyloid beta, which are proteins associated with Alzheimer’s, suggests a third study reported at AAIC 2025.

The researchers exposed human brain cells to lead concentrations of zero, 15 and 50 parts per billion, simulating the kind of lead exposure people might experience through contaminated water or air. The EPA’s action level for lead in drinking water is 15 parts per billion.

They ran molecular, genetic, biochemical and functional tests on the cells and determined that (a) the 15-ppb and 50-ppb lead-exposed neurons were more electrically active (suggesting early dysfunction) than those that had no exposure, (b) energy-producing cells were damaged, and (c) there was an increase in tau and amyloid beta.

Even after the lead was removed, the cells remained primed for damage, responding more severely to additional stressors such as tau.

“These findings help explain how lead exposure, especially in early life or from occupational and environmental sources, might leave a lasting molecular imprint on the brain, making it more vulnerable to age-related diseases like Alzheimer’s,” said Junkai Xie, Ph.D., lead author of the study and post-doctoral research associate in chemical engineering at Purdue University. “Our results show that lead exposure isn’t just a short-term concern; it may set the stage for cognitive problems decades later.”

For the first time, the number of people living with Alzheimer’s disease in the U.S. is more than 7 million. That includes 236,200 in Ohio, according to the 2025 Alzheimer’s Disease Facts and Figures. Deaths due to Alzheimer’s more than doubled (142%) between 2000 and 2022, while deaths from the leading cause of mortality (heart disease) decreased by 2.1%.

In Ohio, there are 452,000 caregivers providing 679 million hours of unpaid care each year, valued at more than $13.3 billion.